package web

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"time"

	"github.com/coreos/go-oidc/v3/oidc"
	"golang.org/x/oauth2"

	"maisym.com/hsa/internal/auth"
	"maisym.com/hsa/internal/classify"
	"maisym.com/hsa/internal/config"
	"maisym.com/hsa/internal/storage"
)

const (
	sessionCookie = "hsa_session"
	loginCookie   = "hsa_login"
)

// Server holds the wired dependencies for the HTTP handlers.
type Server struct {
	cfg        config.Config
	provider   *oidc.Provider
	oauth      *oauth2.Config
	verifier   *oidc.IDTokenVerifier
	store      *storage.Store
	classifier *classify.Classifier // nil when classification is disabled
}

// NewServer performs OIDC discovery against the issuer and builds the server.
// This makes a network call to the issuer's /.well-known/openid-configuration.
// classifier may be nil to disable receipt auto-classification.
func NewServer(ctx context.Context, cfg config.Config, store *storage.Store, classifier *classify.Classifier) (*Server, error) {
	provider, err := oidc.NewProvider(ctx, cfg.IssuerURL)
	if err != nil {
		return nil, fmt.Errorf("oidc discovery against %s: %w", cfg.IssuerURL, err)
	}

	oauthCfg := &oauth2.Config{
		ClientID:     cfg.ClientID,
		ClientSecret: cfg.ClientSecret,
		RedirectURL:  cfg.RedirectURL,
		Endpoint:     provider.Endpoint(),
		Scopes:       []string{oidc.ScopeOpenID, "profile", "email", "groups"},
	}

	return &Server{
		cfg:        cfg,
		provider:   provider,
		oauth:      oauthCfg,
		verifier:   provider.Verifier(&oidc.Config{ClientID: cfg.ClientID}),
		store:      store,
		classifier: classifier,
	}, nil
}

// Routes returns the configured HTTP handler.
func (s *Server) Routes() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /healthz", s.handleHealthz)
	mux.Handle("GET /static/", http.FileServerFS(staticFS))
	mux.HandleFunc("GET /login", s.handleLogin)
	mux.HandleFunc("GET /callback", s.handleCallback)
	mux.HandleFunc("GET /logout", s.handleLogout)
	mux.Handle("GET /{$}", s.requireAuth(http.HandlerFunc(s.handleUploadForm)))
	mux.Handle("POST /upload", s.requireAuth(http.HandlerFunc(s.handleUpload)))
	mux.Handle("POST /classify", s.requireAuth(http.HandlerFunc(s.handleClassify)))
	mux.Handle("GET /duplicates", s.requireAuth(http.HandlerFunc(s.handleDuplicates)))
	mux.Handle("GET /tally", s.requireAuth(http.HandlerFunc(s.handleTally)))
	mux.Handle("GET /recent", s.requireAuth(http.HandlerFunc(s.handleRecentUploads)))
	mux.Handle("GET /recent/receipts", s.requireAuth(http.HandlerFunc(s.handleRecentReceipts)))
	mux.Handle("GET /receipt/{id}/file", s.requireAuth(http.HandlerFunc(s.handleReceiptFile)))
	mux.Handle("GET /attachment/{id}/file", s.requireAuth(http.HandlerFunc(s.handleAttachmentFile)))
	mux.Handle("GET /manage", s.requireAuth(http.HandlerFunc(s.handleManage)))
	mux.Handle("POST /manage/categories", s.requireAuth(http.HandlerFunc(s.handleAddCategory)))
	mux.Handle("POST /manage/categories/rename", s.requireAuth(http.HandlerFunc(s.handleRenameCategory)))
	mux.Handle("POST /manage/people", s.requireAuth(http.HandlerFunc(s.handleAddPerson)))
	mux.Handle("POST /manage/people/rename", s.requireAuth(http.HandlerFunc(s.handleRenamePerson)))
	mux.Handle("GET /export", s.requireAuth(http.HandlerFunc(s.handleExportPage)))
	mux.Handle("GET /export/db", s.requireAuth(http.HandlerFunc(s.handleExportDB)))
	return mux
}

func (s *Server) handleHealthz(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
	fmt.Fprintln(w, "ok")
}

// handleLogin starts the OIDC flow: generate PKCE + state + nonce, stash them in
// a short-lived encrypted cookie, and redirect to Authelia's authorize endpoint.
func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
	verifier, err := auth.GenerateVerifier()
	if err != nil {
		s.serverError(w, "generate verifier", err)
		return
	}
	state, err := auth.GenerateState()
	if err != nil {
		s.serverError(w, "generate state", err)
		return
	}
	nonce, err := auth.GenerateState() // reuse the random generator for the nonce
	if err != nil {
		s.serverError(w, "generate nonce", err)
		return
	}

	ls := auth.LoginState{State: state, Verifier: verifier, Nonce: nonce}
	encoded, err := auth.EncodeLoginState(ls, s.cfg.SessionKey)
	if err != nil {
		s.serverError(w, "encode login state", err)
		return
	}
	s.setCookie(w, loginCookie, encoded, 10*time.Minute)

	challenge := auth.ChallengeS256(verifier)
	url := auth.AuthorizeURL(s.oauth, state, challenge, oidc.Nonce(nonce))
	http.Redirect(w, r, url, http.StatusFound)
}

// handleCallback completes the OIDC flow: validate state, exchange the code with
// PKCE, verify the ID token, check the group, and set the session cookie.
func (s *Server) handleCallback(w http.ResponseWriter, r *http.Request) {
	// Recover the login state from the cookie.
	c, err := r.Cookie(loginCookie)
	if err != nil {
		http.Error(w, "missing login state; start at /login", http.StatusBadRequest)
		return
	}
	ls, err := auth.DecodeLoginState(c.Value, s.cfg.SessionKey)
	if err != nil {
		http.Error(w, "invalid login state", http.StatusBadRequest)
		return
	}
	s.clearCookie(w, loginCookie)

	// CSRF: the state we issued must match the one returned.
	if r.URL.Query().Get("state") != ls.State {
		http.Error(w, "state mismatch", http.StatusBadRequest)
		return
	}

	// Exchange the authorization code, sending the PKCE verifier.
	code := r.URL.Query().Get("code")
	token, err := s.oauth.Exchange(r.Context(), code, oauth2.VerifierOption(ls.Verifier))
	if err != nil {
		s.serverError(w, "token exchange", err)
		return
	}

	rawIDToken, ok := token.Extra("id_token").(string)
	if !ok {
		http.Error(w, "no id_token in response", http.StatusBadGateway)
		return
	}
	idToken, err := s.verifier.Verify(r.Context(), rawIDToken)
	if err != nil {
		s.serverError(w, "verify id_token", err)
		return
	}
	if idToken.Nonce != ls.Nonce {
		http.Error(w, "nonce mismatch", http.StatusBadRequest)
		return
	}

	// Authelia serves groups/email from the UserInfo endpoint rather than the ID
	// token by default, so read claims from the ID token and merge in UserInfo.
	type oidcClaims struct {
		Email             string   `json:"email"`
		PreferredUsername string   `json:"preferred_username"`
		Groups            []string `json:"groups"`
	}
	var idClaims oidcClaims
	if err := idToken.Claims(&idClaims); err != nil {
		s.serverError(w, "parse id token claims", err)
		return
	}

	var uiClaims oidcClaims
	if userInfo, err := s.provider.UserInfo(r.Context(), oauth2.StaticTokenSource(token)); err == nil {
		_ = userInfo.Claims(&uiClaims)
	} else {
		log.Printf("warning: userinfo fetch failed: %v", err)
	}

	groups := idClaims.Groups
	if len(groups) == 0 {
		groups = uiClaims.Groups
	}
	email := idClaims.Email
	if email == "" {
		email = uiClaims.Email
	}
	username := idClaims.PreferredUsername
	if username == "" {
		username = uiClaims.PreferredUsername
	}

	subject := email
	if subject == "" {
		subject = username
	}
	log.Printf("login attempt: subject=%q groups=%v", subject, groups)

	// Authorization gate: must be in the required group.
	if !auth.IsAuthorized(groups, s.cfg.RequiredGroup) {
		http.Error(w, fmt.Sprintf("403: not a member of %q", s.cfg.RequiredGroup), http.StatusForbidden)
		return
	}

	sess := auth.Session{Subject: subject, Groups: groups, IssuedAt: time.Now().UTC()}
	encoded, err := auth.EncodeSession(sess, s.cfg.SessionKey)
	if err != nil {
		s.serverError(w, "encode session", err)
		return
	}
	s.setCookie(w, sessionCookie, encoded, 12*time.Hour)
	http.Redirect(w, r, "/", http.StatusFound)
}

func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	s.clearCookie(w, sessionCookie)
	http.Redirect(w, r, "/login", http.StatusFound)
}

func (s *Server) serverError(w http.ResponseWriter, what string, err error) {
	log.Printf("error: %s: %v", what, err)
	http.Error(w, "internal server error", http.StatusInternalServerError)
}